Add support for base address entries in the .debug_ranges section

[tberghammer]

Summary

Clang recently started to emit base address entries into the
.debug_ranges section to reduce the number of relocations needed. Lets
make sure LLDB can read them.

[tberghammer]

Submitted as rL309554 to get the buildbot using ToT clang green again but if you have any comment then let me know and I will address it in a followup CL.

[clayborg]

I was out on vacation, sorry for the delay. Looks good.

source/Plugins/SymbolFile/DWARF/DWARFDebugRanges.cpp

 #include "DWARFDebugRanges.h"
 #include "SymbolFileDWARF.h"
 #include "lldb/Utility/Stream.h"
 #include <assert.h>
 
 using namespace lldb_private;
 using namespace std;
 
+static dw_addr_t GetBaseAddressMarker(uint32_t addr_size) {
+  switch(addr_size) {
+    case 2:
+      return 0xffff;
+    case 4:
+      return 0xffffffff;
+    case 8:
+      return 0xffffffffffffffff;
+  }
+  llvm_unreachable("GetBaseAddressMarker unsupported address size.");
+}
+
 DWARFDebugRanges::DWARFDebugRanges() : m_range_map() {}
 
 DWARFDebugRanges::~DWARFDebugRanges() {}
 
 void DWARFDebugRanges::Extract(SymbolFileDWARF *dwarf2Data) {
   DWARFRangeList range_list;
   lldb::offset_t offset = 0;
   dw_offset_t debug_ranges_offset = offset;
   while (Extract(dwarf2Data, &offset, range_list)) {
     range_list.Sort();
     m_range_map[debug_ranges_offset] = range_list;
     debug_ranges_offset = offset;
   }
 }
 
 bool DWARFDebugRanges::Extract(SymbolFileDWARF *dwarf2Data,
                                lldb::offset_t *offset_ptr,
                                DWARFRangeList &range_list) {
   range_list.Clear();
 
   lldb::offset_t range_offset = *offset_ptr;
   const DWARFDataExtractor &debug_ranges_data =
       dwarf2Data->get_debug_ranges_data();
   uint32_t addr_size = debug_ranges_data.GetAddressByteSize();
+  dw_addr_t base_addr = 0;
+  dw_addr_t base_addr_marker = GetBaseAddressMarker(addr_size);
 
   while (
       debug_ranges_data.ValidOffsetForDataOfSize(*offset_ptr, 2 * addr_size)) {
     dw_addr_t begin = debug_ranges_data.GetMaxU64(offset_ptr, addr_size);
     dw_addr_t end = debug_ranges_data.GetMaxU64(offset_ptr, addr_size);
+
     if (!begin && !end) {
       // End of range list
       break;
     }
-    // Extend 4 byte addresses that consists of 32 bits of 1's to be 64 bits
-    // of ones
-    switch (addr_size) {
-    case 2:
-      if (begin == 0xFFFFull)
-        begin = LLDB_INVALID_ADDRESS;
-      break;
 
-    case 4:
-      if (begin == 0xFFFFFFFFull)
-        begin = LLDB_INVALID_ADDRESS;
-      break;
-
-    case 8:
-      break;
-
-    default:
-      llvm_unreachable("DWARFRangeList::Extract() unsupported address size.");
+    if (begin == base_addr_marker) {
+      base_addr = end;
+      continue;
     }
 
     // Filter out empty ranges
     if (begin < end)
-      range_list.Append(DWARFRangeList::Entry(begin, end - begin));
+      range_list.Append(DWARFRangeList::Entry(begin + base_addr, end - begin));
   }
 
   // Make sure we consumed at least something
   return range_offset != *offset_ptr;
 }
 
 void DWARFDebugRanges::Dump(Stream &s,
                             const DWARFDataExtractor &debug_ranges_data,